If 1-x gm of seawater of concentration c is mixed adia,batica,lly with 

 X gm of concentration c + A c (both at a temperature t), the temperature 

 of the mixture T^ will differ from the temperature before mixing. The 



concentration of the mixture is c + x Ac, and its specific hea,t content is 



h (Tf, c + X Ac) = (1-x Ac) h^(T,c) + x Ac h^(T) + x (2cAc +A c ) h.^{'^)/2. (?) 



The specific heat content of the mixture at the original temperature 

 T is: 



h (t,c + xAc) = (l-xAc) h^(T,c) + xAc h^(T) + (xAc + 2cAc) ^^(t) /2 (8) 



The change in temperature T„ -T is therefore 



T -T = h(T^, c + xAc) - h(T, c + xAc) = + x(l-x) Ac^ ^^(t)/ 2C,p (9) 

 _ 



P 



The temperature change on mixing two isothermal batches of seawater thus 

 depends only on the value of the term h and is proportional to the 



square of the concentration difference. 



The seawaters mixed were 6O.O with 10.0, 5U.6 with I5.O, kS .G with 20.0, 

 and ^5-^ with 2h. Q°loo • They were made according to the formula and procedure 

 of Kester, et al. (1967). The salinities were determined by the Mohr method 

 of chloride titration; and, for the high salinity water, dilution a,nd 

 conductivity measurements were made. The silver nitrate solution used was 

 standardized against I.A.P.O. standard seawater. The results are given 

 in Table 1, a,nd a plot of Yv versus x(l-x)/|j c^ is shown in Figure 3- Within 

 a,n estimated experimental error of ±5io, Figure 3 indicates that the slope 

 ii of the linear equation for h is constant over the concentration ra,nge 

 from 6ofoe. to ia/o« . ^ 



The optimum salinities for determining the heat of mixing as a function 

 of temperature a,re then lO^o and 60^o . Therefore, a series of mixing 

 experiments were carried out at various temperatures between 2° and 25.3°C 

 on seawa,ter of 10.2%o and GO.3%0 salinity. The results are presented in 

 Table 2 and a.re shown graphically in Figure k. 



The empirical equation f or /\ T as a function of T is 



aT = -0.0736 + 3.11*10"^T - 1+.72'10"^T^. (10) 



Equation (lO) can be substituted into equation (9) to obtain ii as a 

 function of temperature. Finally, h and h can be evaluated From 

 heat capacity data to obtain an empirical equation for the enthalpy c 

 seawater (equation 5) as a, function of temperature and salinity. 



431 



